If, after 30 days, you haven't chosen and selected a Most Helpful opinion, one will automatically be chosen for you.Neither the Question Asker nor the user awarded Most Helpful will get Xper points for these automatic selections.It's chosen based on engagement: votes, comments, length, time, xper level, gender, among other criteria. As long as you're giving helpful opinions, we'll find them!

I usually wait till I think I've got a good handful of opinions so that way it's fair but then I just pick one if one of them stands out to me otherwise I just wait to get that message from GaG to do it.